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<pre><span class="sourceLineNo">001</span><a name="line.1"></a>
<span class="sourceLineNo">002</span>/*<a name="line.2"></a>
<span class="sourceLineNo">003</span> * Copyright (C) 2014 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<span class="sourceLineNo">004</span> *<a name="line.4"></a>
<span class="sourceLineNo">005</span> * $Id: KeyListEncoder.html 939 2015-05-29 01:16:17Z archie.cobbs $<a name="line.5"></a>
<span class="sourceLineNo">006</span> */<a name="line.6"></a>
<span class="sourceLineNo">007</span><a name="line.7"></a>
<span class="sourceLineNo">008</span>package org.jsimpledb.kv.util;<a name="line.8"></a>
<span class="sourceLineNo">009</span><a name="line.9"></a>
<span class="sourceLineNo">010</span>import com.google.common.base.Preconditions;<a name="line.10"></a>
<span class="sourceLineNo">011</span><a name="line.11"></a>
<span class="sourceLineNo">012</span>import java.io.EOFException;<a name="line.12"></a>
<span class="sourceLineNo">013</span>import java.io.IOException;<a name="line.13"></a>
<span class="sourceLineNo">014</span>import java.io.InputStream;<a name="line.14"></a>
<span class="sourceLineNo">015</span>import java.io.OutputStream;<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>import org.jsimpledb.util.LongEncoder;<a name="line.17"></a>
<span class="sourceLineNo">018</span>import org.jsimpledb.util.UnsignedIntEncoder;<a name="line.18"></a>
<span class="sourceLineNo">019</span><a name="line.19"></a>
<span class="sourceLineNo">020</span>/**<a name="line.20"></a>
<span class="sourceLineNo">021</span> * Serializes a sequence of {@code byte[]} arrays, compressing common prefixes.<a name="line.21"></a>
<span class="sourceLineNo">022</span> *<a name="line.22"></a>
<span class="sourceLineNo">023</span> * &lt;p&gt;<a name="line.23"></a>
<span class="sourceLineNo">024</span> * Keys are encoded in one of two forms:<a name="line.24"></a>
<span class="sourceLineNo">025</span> *  &lt;ul&gt;<a name="line.25"></a>
<span class="sourceLineNo">026</span> *  &lt;li&gt;{@code total-length bytes...}<a name="line.26"></a>
<span class="sourceLineNo">027</span> *  &lt;li&gt;{@code -prefix-length suffix-length suffix-bytes ...}<a name="line.27"></a>
<span class="sourceLineNo">028</span> *  &lt;/ul&gt;<a name="line.28"></a>
<span class="sourceLineNo">029</span> * The first length ({@code total-length} or negative {@code prefix-length}) is encoded using {@link LongEncoder}.<a name="line.29"></a>
<span class="sourceLineNo">030</span> * The {@code suffix-length}, if present, is encoded using {@link UnsignedIntEncoder}.<a name="line.30"></a>
<span class="sourceLineNo">031</span> */<a name="line.31"></a>
<span class="sourceLineNo">032</span>public final class KeyListEncoder {<a name="line.32"></a>
<span class="sourceLineNo">033</span><a name="line.33"></a>
<span class="sourceLineNo">034</span>    private KeyListEncoder() {<a name="line.34"></a>
<span class="sourceLineNo">035</span>    }<a name="line.35"></a>
<span class="sourceLineNo">036</span><a name="line.36"></a>
<span class="sourceLineNo">037</span>    /**<a name="line.37"></a>
<span class="sourceLineNo">038</span>     * Write the next key, compressing its common prefix with the previous key (if any).<a name="line.38"></a>
<span class="sourceLineNo">039</span>     *<a name="line.39"></a>
<span class="sourceLineNo">040</span>     * @param out output stream<a name="line.40"></a>
<span class="sourceLineNo">041</span>     * @param key key to write<a name="line.41"></a>
<span class="sourceLineNo">042</span>     * @param prev previous key, or null for none<a name="line.42"></a>
<span class="sourceLineNo">043</span>     * @throws IOException if an I/O error occurs<a name="line.43"></a>
<span class="sourceLineNo">044</span>     * @throws IllegalArgumentException if {@code out} or {@code key} is null<a name="line.44"></a>
<span class="sourceLineNo">045</span>     */<a name="line.45"></a>
<span class="sourceLineNo">046</span>    public static void write(OutputStream out, byte[] key, byte[] prev) throws IOException {<a name="line.46"></a>
<span class="sourceLineNo">047</span>        Preconditions.checkArgument(out != null, "null out");<a name="line.47"></a>
<span class="sourceLineNo">048</span>        Preconditions.checkArgument(key != null, "null key");<a name="line.48"></a>
<span class="sourceLineNo">049</span>        int prefixLength = 0;<a name="line.49"></a>
<span class="sourceLineNo">050</span>        if (prev != null) {<a name="line.50"></a>
<span class="sourceLineNo">051</span>            while (prefixLength &lt; key.length &amp;&amp; prefixLength &lt; prev.length &amp;&amp; key[prefixLength] == prev[prefixLength])<a name="line.51"></a>
<span class="sourceLineNo">052</span>                prefixLength++;<a name="line.52"></a>
<span class="sourceLineNo">053</span>        }<a name="line.53"></a>
<span class="sourceLineNo">054</span>        if (prefixLength &gt; 1) {<a name="line.54"></a>
<span class="sourceLineNo">055</span>            final int suffixLength = key.length - prefixLength;<a name="line.55"></a>
<span class="sourceLineNo">056</span>            LongEncoder.write(out, ~(prefixLength - 2));<a name="line.56"></a>
<span class="sourceLineNo">057</span>            UnsignedIntEncoder.write(out, suffixLength);<a name="line.57"></a>
<span class="sourceLineNo">058</span>            out.write(key, prefixLength, suffixLength);<a name="line.58"></a>
<span class="sourceLineNo">059</span>        } else {<a name="line.59"></a>
<span class="sourceLineNo">060</span>            LongEncoder.write(out, key.length);<a name="line.60"></a>
<span class="sourceLineNo">061</span>            out.write(key);<a name="line.61"></a>
<span class="sourceLineNo">062</span>        }<a name="line.62"></a>
<span class="sourceLineNo">063</span>    }<a name="line.63"></a>
<span class="sourceLineNo">064</span><a name="line.64"></a>
<span class="sourceLineNo">065</span>    /**<a name="line.65"></a>
<span class="sourceLineNo">066</span>     * Calculate the number of bytes that would be required to write the next key via {@link #write write()}.<a name="line.66"></a>
<span class="sourceLineNo">067</span>     *<a name="line.67"></a>
<span class="sourceLineNo">068</span>     * @param key key to write<a name="line.68"></a>
<span class="sourceLineNo">069</span>     * @param prev previous key, or null for none<a name="line.69"></a>
<span class="sourceLineNo">070</span>     * @return number of bytes to be written by {@link #write write(out, key, prev)}<a name="line.70"></a>
<span class="sourceLineNo">071</span>     * @throws IllegalArgumentException if {@code key} is null<a name="line.71"></a>
<span class="sourceLineNo">072</span>     */<a name="line.72"></a>
<span class="sourceLineNo">073</span>    public static int writeLength(byte[] key, byte[] prev) {<a name="line.73"></a>
<span class="sourceLineNo">074</span>        Preconditions.checkArgument(key != null, "null key");<a name="line.74"></a>
<span class="sourceLineNo">075</span>        int prefixLength = 0;<a name="line.75"></a>
<span class="sourceLineNo">076</span>        if (prev != null) {<a name="line.76"></a>
<span class="sourceLineNo">077</span>            while (prefixLength &lt; key.length &amp;&amp; prefixLength &lt; prev.length &amp;&amp; key[prefixLength] == prev[prefixLength])<a name="line.77"></a>
<span class="sourceLineNo">078</span>                prefixLength++;<a name="line.78"></a>
<span class="sourceLineNo">079</span>        }<a name="line.79"></a>
<span class="sourceLineNo">080</span>        if (prefixLength &gt; 1) {<a name="line.80"></a>
<span class="sourceLineNo">081</span>            final int suffixLength = key.length - prefixLength;<a name="line.81"></a>
<span class="sourceLineNo">082</span>            return LongEncoder.encodeLength(~(prefixLength - 2)) + UnsignedIntEncoder.encodeLength(suffixLength) + suffixLength;<a name="line.82"></a>
<span class="sourceLineNo">083</span>        } else<a name="line.83"></a>
<span class="sourceLineNo">084</span>            return LongEncoder.encodeLength(key.length) + key.length;<a name="line.84"></a>
<span class="sourceLineNo">085</span>    }<a name="line.85"></a>
<span class="sourceLineNo">086</span><a name="line.86"></a>
<span class="sourceLineNo">087</span>    /**<a name="line.87"></a>
<span class="sourceLineNo">088</span>     * Read the next key.<a name="line.88"></a>
<span class="sourceLineNo">089</span>     *<a name="line.89"></a>
<span class="sourceLineNo">090</span>     * @param input input stream<a name="line.90"></a>
<span class="sourceLineNo">091</span>     * @param prev previous key, or null for none<a name="line.91"></a>
<span class="sourceLineNo">092</span>     * @return next key<a name="line.92"></a>
<span class="sourceLineNo">093</span>     * @throws IOException if an I/O error occurs<a name="line.93"></a>
<span class="sourceLineNo">094</span>     * @throws EOFException if an unexpected EOF is encountered<a name="line.94"></a>
<span class="sourceLineNo">095</span>     * @throws IllegalArgumentException if {@code input} is null<a name="line.95"></a>
<span class="sourceLineNo">096</span>     * @throws IllegalArgumentException if {@code input} contains invalid data<a name="line.96"></a>
<span class="sourceLineNo">097</span>     */<a name="line.97"></a>
<span class="sourceLineNo">098</span>    public static byte[] read(InputStream input, byte[] prev) throws IOException {<a name="line.98"></a>
<span class="sourceLineNo">099</span>        Preconditions.checkArgument(input != null, "null input");<a name="line.99"></a>
<span class="sourceLineNo">100</span><a name="line.100"></a>
<span class="sourceLineNo">101</span>        // Get encoded length of prefix<a name="line.101"></a>
<span class="sourceLineNo">102</span>        int keyLength = KeyListEncoder.readSignedInt(input);<a name="line.102"></a>
<span class="sourceLineNo">103</span>        final byte[] key;<a name="line.103"></a>
<span class="sourceLineNo">104</span>        int prefixLength;<a name="line.104"></a>
<span class="sourceLineNo">105</span><a name="line.105"></a>
<span class="sourceLineNo">106</span>        // Decode prefix length and read prefix, if any<a name="line.106"></a>
<span class="sourceLineNo">107</span>        if (keyLength &lt; 0) {<a name="line.107"></a>
<span class="sourceLineNo">108</span>            if (prev == null)<a name="line.108"></a>
<span class="sourceLineNo">109</span>                throw new IllegalArgumentException("null `prev' given but next key has " + -keyLength + " byte shared prefix");<a name="line.109"></a>
<span class="sourceLineNo">110</span>            prefixLength = ~keyLength + 2;<a name="line.110"></a>
<span class="sourceLineNo">111</span>            final int suffixLength = UnsignedIntEncoder.read(input);<a name="line.111"></a>
<span class="sourceLineNo">112</span>            keyLength = prefixLength + suffixLength;<a name="line.112"></a>
<span class="sourceLineNo">113</span>            if (keyLength &lt; 0)<a name="line.113"></a>
<span class="sourceLineNo">114</span>                throw new IllegalArgumentException("invalid prefix length " + prefixLength + " plus suffix length " + suffixLength);<a name="line.114"></a>
<span class="sourceLineNo">115</span>            key = new byte[keyLength];<a name="line.115"></a>
<span class="sourceLineNo">116</span>            System.arraycopy(prev, 0, key, 0, prefixLength);<a name="line.116"></a>
<span class="sourceLineNo">117</span>        } else {<a name="line.117"></a>
<span class="sourceLineNo">118</span>            key = new byte[keyLength];<a name="line.118"></a>
<span class="sourceLineNo">119</span>            prefixLength = 0;<a name="line.119"></a>
<span class="sourceLineNo">120</span>        }<a name="line.120"></a>
<span class="sourceLineNo">121</span><a name="line.121"></a>
<span class="sourceLineNo">122</span>        // Read suffix<a name="line.122"></a>
<span class="sourceLineNo">123</span>        while (prefixLength &lt; key.length) {<a name="line.123"></a>
<span class="sourceLineNo">124</span>            final int num = input.read(key, prefixLength, key.length - prefixLength);<a name="line.124"></a>
<span class="sourceLineNo">125</span>            if (num == -1)<a name="line.125"></a>
<span class="sourceLineNo">126</span>                throw new EOFException();<a name="line.126"></a>
<span class="sourceLineNo">127</span>            prefixLength += num;<a name="line.127"></a>
<span class="sourceLineNo">128</span>        }<a name="line.128"></a>
<span class="sourceLineNo">129</span><a name="line.129"></a>
<span class="sourceLineNo">130</span>        // Done<a name="line.130"></a>
<span class="sourceLineNo">131</span>        return key;<a name="line.131"></a>
<span class="sourceLineNo">132</span>    }<a name="line.132"></a>
<span class="sourceLineNo">133</span><a name="line.133"></a>
<span class="sourceLineNo">134</span>    private static int readSignedInt(InputStream input) throws IOException {<a name="line.134"></a>
<span class="sourceLineNo">135</span>        final long longValue = LongEncoder.read(input);<a name="line.135"></a>
<span class="sourceLineNo">136</span>        final int intValue = (int)longValue;<a name="line.136"></a>
<span class="sourceLineNo">137</span>        Preconditions.checkArgument(intValue == (int)longValue, "read out-of-range encoded int value %s", longValue);<a name="line.137"></a>
<span class="sourceLineNo">138</span>        return intValue;<a name="line.138"></a>
<span class="sourceLineNo">139</span>    }<a name="line.139"></a>
<span class="sourceLineNo">140</span>}<a name="line.140"></a>
<span class="sourceLineNo">141</span><a name="line.141"></a>




























































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